Problem: $ C = \left[\begin{array}{rrrr}1 & 0 & -2 & 0 \\ 0 & 2 & 0 & 1 \\ -1 & 4 & -1 & 1 \\ 1 & -2 & -2 & 4\end{array}\right]$ What are the dimensions of matrix $ C$ ?
Solution: The first dimension is the number of rows in the matrix. How many rows does $ C$ have? The second dimension is the number of columns in the matrix. How many columns does $ C$ have? So, $ C$ is a 4 $\times$ 4 matrix.